Polyether polyurethane moldings are being increasingly used in the manufacture of automobiles, furniture and in home construction. Molded polyether polyurethanes are especially important because they are lightweight and are resistant to moisture, weather, temperature extremes, and aging. As an illustration, molded polyether polyurethane elastomers have become of special interest in the manufacture of force-reducing impact media such as safety impact bumpers for automotive vehicles and impact-resistant automotive fascia.
The high demand for molded polyether polyurethane articles requires that they be produced in the largest numbers in the shortest possible time. Polyurethane-forming mixtures are eminently suited for mass production because the reactants are liquid, that is they are pumpable, and are quick-reacting. The problem has existed, however, in providing adequate mold release in the shortest possible time to take fullest advantage of the unique capabilities of the polyurethane systems.
This invention relates to the improved release of polyurethane compositions from molds in which they are formed and shaped as well as to polyol compositions suitable for such use.
Heretofore, release of molded articles from molds in which they have been formed has been achieved by coating the surface of the mold cavity with an agent which facilitates release of the molded article from the walls of the mold cavity. Procedures such as this are described in U.S. Pat. Nos. 3,694,530, 3,640,769, 3,624,190, 3,607,397 and 3,413,390. This method has certain disadvantages. The agent, after molding, adheres to the surface of the molded article thereby removing such from the surface of the mold. As the mold release agent is removed from the mold surface, it must therefore be replaced so as to provide continued release of the molded articles from the mold. The necessity for repeated additions of mold release agent results in additional expense due to low productivity as a result of the additional time incurred in applying such additional quantities of mold release agents to the mold surfaces.
In addition, mold build-up may become a problem, since a fine film of urethane is left in spot areas of the mold surface. This build-ups on the surface of the mold cavity walls and eventually covers and obscures any detail on the mold cavity surface desired to be imparted to the molded article. Also, the presence of the release agent adhering to the surface of the molded article can impede subsequent operations on the article, such as painting or adhering operations. While it is possible to clean the surfaces of molded articles in preparation for painting or adhering operations, this adds to the time and expense of production.
Additionally, the need to reapply the release agent after each molding or a limited number of moldings interrupts the molding operation and slows down output.
The use of internal mold release agents for use in molding polyurethane articles has been disclosed by Boden et al in U.S. Pat. No. 3,726,952, Godlewski in U.S. Pat. No. 4,024,088, Bonin et al. in U.S. Pat. No. 4,098,731, Sparrow et al. in U.S. Pat. No. 4,130,698, Godlewski in U.S. Pat. No. 4,111,861, Kleimann et al. in U.S. Pat. No. 4,201,847 and Godlewski in U.S. Pat. No. 4,220,727.
Many of these internal mold release agents bleed or creep to the surface of the molded article necessitating a removal operation before such articles can be painted. Other are incompatible with polyether polyols and/or reduce the activity of the catalyst.
The present invention is therefore more particularly directed to the use of internal mold release agents which do not bleed or creep to the surface of the molded article which results in either the inability to paint the surface of the article or else the surface of the article must be treated prior to painting thereof. These mold release agents also do not significantly affect the activity of the catalysts employed.
The term active hydrogen as employed herein means that the hydrogen atom has sufficient activity so as to react with an --NCO and/or --NCS group in the presence of suitable catalyst.
The term polyurethane as employed herein refers to any product resulting from the reaction of a material containing an average of more than one active hydrogen atom per molecule and a material having an average of more than one --NCO and/or --NCS group per molecule.